This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We and others have postulated that inflammation plays a role in the pathogenesis of Lyme neuroborreliosis. Borrelia burgdorferi (Bb) is the bacterial spirochete that causes Lyme disease and is known to induce the production of inflammatory mediators in glial cells. In experiments where Bb was co-cultured in vitro with microglial cells isolated from primary rhesus cortex, we observed robust expression and release of the inflammatory cytokines/chemokines IL-6 and 8, MIP-1[unreadable], MIP-1[unreadable], RANTES and MCP-1 but we detected no concomitant induction of microglial apoptosis. SH-SY5Y (SY) neurons independently co-cultured with Bb expressed negligible amounts of inflammatory molecules and were also highly resistant to apoptosis. In contrast, when microglia were combined with SY cells and then co-cultivated with Bb, significant increases in apoptosis consistently occurred. Confocal microscopy images of the mixed cultures stained for apoptosis by the TUNEL assay and with cell specific markers suggested that it was predominantly the neuronal type cells that were dying in response to stimulation with Bb. Microarray analysis demonstrated that in addition to the inflammatory mediators secreted by microglia in response to Bb, increased expression of TLR2 and NFKB1 transcripts were also observed and may additionally contribute to a neurotoxic environment. Taken together, these findings indicate that Bb is not directly toxic to neurons;rather, neurons become impaired/die in the inflammatory surroundings generated by microglial cells through a bystander effect. This neuronal impairment may eventually contribute to the neurocognitive symptoms seen in neuroborreliosis.